Loaded electric circuit.



N0 140mm,

PATENT-ED JUNE 2; 1903.

1-1. s. WARREN & G. A. CAMPBELL. LOADED ELECTRIC CIRCUIT.

APPLICATION FILED MAR. 19, 1902.

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UNITED STATES Patented June 2, 1903.

PATENT FFICE.

I HOWARD WARREN, OF EVERETT, AN GEORGE A; CAMPBELL, O EW- TON,MASSACHUSETTS, AssIeN s [IO AMERICAN TELEPHONE ANDJrELE- GRAPH-OOMPANY ACORPORATION OF NEW YORK.- l

LOADED ELECTRIC CIRCUIT.

SPECIFIOATIQN forming part of Letters Batent No. 729,709, dated June 2,1903. Application filed March 19, 1902- Serial No. 98,933. (No model.)

To all whom it may co7tcc7 n:

Be it known that we,"HOWARDS.WARREN, residing at Everett, and GEORGE A.CAMP- BELL, residing at Newton, in the county of Middlesex and State ofMassachusetts, have invented certain Improvements in Loaded ElectricCircuits, of which the following is a specification. This inventionconcerns electric circuits ro loaded with inductance-coils for thepreveng portion of the circuit having a well-definedcharacter to anotherof diverse characteriza tion a reflection of the waves occurs at thepoint of heterogeneity and the reflected waves tend to travel back totheir place of origin instead of proceeding to the farther end of thecircuit. Experience has demonstrated that when a comparatively shortportion of i "unloaded extension or continuation circuit conductor isattached to the end of a long loaded circuit or line a decided loss ofeffi- 3o ciency in transmission over the said loaded line occurs. In theoperation, for instance, of telephone-circuits the telephone instrumentsof a user or of a subscribers station are not usually united directly toa loaded long-distance circuit conductor, the connec-- tion with suchloaded-circuit conductor being generally established through theunloaded conductors of the subscribers line-circuit and frequently alsothrough the conductors '40 of a trunk-line or other intervening circuitconnection. Under such conditions ade'pre ciation of transmissionefficiency is clearly manifested and is due to'the reflection lossesaccruingfrom the abrupttransition between 5 the high impedance oftlieloaded line and the low impedance of the unloaded portion of the circuitextending from the loaded line to the said station instruments.

The object of this invention is to prevent these reflection losses byproviding effectual and easily-applied means for the avoidance of suchabrupt changes in the character of the circuit.

Accordingly the invention consists in a localized and artificialimpedance taper or 'taa q pering system adapted to be interposed betweenthe regularlyeloaded main-line conductor and any such extension orcontinuation circuit conductor as mayat or through a terminal or waystation extend to the oper- 6o 1 ating instruments of a substation, or,to state the matter otherwise, between such loaded line portion and thestation instruments regardless of the presence, absence, or length coilsconnected in .series in a circuit-conductor adapted to be placed in acombined circuit between the regularly-loaded portion and the station orcontinuation circuit and a group of associated condensers in parallelbranches of said circuit-conductor, the inductances of said coils andthe capacities of said condensers being so arranged and relativelyproportioned as to provide a succession of sections or elements ofgradually or pro gressively changing impedance, the different values ofsaid impedance-sections of course increasing as they progress toward theloaded portion of the line and diminishing as respects transmission fromsuch loaded portion ofthe circuit and toward the unload ed portionthereof. The condenser branches extend from points between theself-induction coils or, if

desired, from the center of the coils to the return conductor of thecircuit, and the coils 5 themselves may be wound over separate ironcores or over diiferent sections of the same core.

The invention consists, further, in combining the localized artificialload or impedance tapering apparatus or system with a loaded electriccircuit in such manner that when the said apparatus is placed betweensaid loaded circuit and an unloaded continuation thereof there shall bea graded fall or a fall in pro gressive relatively short steps from theimpedance of the loaded circuit to that of its unloaded continuation,andthis whether the said unloaded continuation be located at a terminalstation or at a way-station.

In the drawings which accompany and illustrate this specification,Figure l is a diagram conventionally representing a long loaded circuitconnecting at each end with an unloaded portion of a circuit andtelephone instruments through our localized and artificial taperingapparatus. Fig. 2 represents one end of such a circuit connected withterminal telephone instruments through such a concentrated terminaltaper wherein the inducto-resistance elements are wound on separate andindependent cores. Fig. 3 represents an example ofa localized taperingap-- paratus in which the inductance-coils of the graduated impedanceare wound over separate sections of the same iron core, and Figs. 4, 5,and 6 are diagrams representing different plans for utilizing thelocalized tapering appliances or apparatus at way-stations.

In Fig. 1, L is the mainline or portion of the.

circuit having main conductors 2 and 3 and loading inductancecoils O, SS the instruments of' stations (usually substations) connected therewithat the two ends thereof, and UU intermediate unloaded portions ofthecircuit as completed between the two sets of telephone or otherinstruments, such portions consisting, as the case may be, of asubstationcircuit or of a station-circuit and an intervening trunk-line.The station instruments may, as shown, comprise the receivers T T thetransmitters i 25 the batteries 1) for said transmitters, and theinduction-coils I, having each a primary winding 5 in a local circuitwith the transmitter electrodes and battery, and a secondary winding 71in the main line, together with the receiver. A and B at the two ends,respectively, of the loaded line are the localized load taperingappliances placed at suitable stations at the ends of saidline andinterposed between the regularlyloaded permanent portion L of thecircuit and the unloaded extension or continuation portions thereof, U Uleading ultimately to the station instruments S S Being thus placed,they are properly described as being between the loaded portion of thecircuit and the said instruments S S The broken lines at d 01 indicatethat at these points the loaded long-' distance lines terminate, and thebroken lines e e afford a similar indication as re= gards the circuitcontinuations U U leading ratio between successive sections.

to the station instruments S S The said lo calized load-taperingapparatus may otherwise be described as an artificial loaded andgraduated reflection-reducing extension of the loaded portion of thecircuit and comprises the circuit-conductors 4 5, which end at D and E,respectively, the diverse inductance and resistance coils H H H 850.united serially by said conductors with one another, (and with theloaded line L and instruments S S and the condensers 7o Z0 7%, &c.,placed, as shown, in parallel branches or bridges between the two maincircuit-conductors, or, as a matter of course, in the case of a groundedmain circuit extending from the main conductor to its earth return. Itwill be thus seen that the localized taper apparatus of this inventionis practically an artificial intermediary connection forming a portionof the completed circuit, which being located at a suitable stationbetween the otherwise immediately adjacent loaded and unloaded portionsof the said circuit may be always concentrated and always undercontroland supervision and which is formed of and provided withsuccessive graduated impedance sections or elements steppinggraduallydown or tapering from the section nearest the loaded line, theimpedance value of which approximates that of a like section of loadedline to the section nearest the unloaded portion of the circuit orinstrument continuation, which section has an impedance value in likemanner closely approaching that of such terminal or continuation. Thedrawings show three such graded impedance-sections; but it is of courseto be understood that the invention is not limited or restricted to anyparticular number thereof and that the number and value of .the saidsteps or sections may be varied within a wide range, depending largelyupon the peculiar conditions of any particular case. Assuming, forexample, that the impedance of a given length (corresponding to asection of the taper) of the loaded main-line portion of the circuitis'three thousand ohms and that the tapering apparatus or system is tocomprise, say, six sections, the impedance values progressivelydiminishing toward the u nloaded portion of the circuit will thenpreferably be two thousand four hundred, eighteen hundred and fifty,fourteen hundred and twentyfive, eleven hundred, eight hundred andfifty, and six hundred and fifty ohms, respectively, thus following asubstantially geometrical It is to be observed that in such a taperingapparatus it is the property or characteristic of impedance whichrequires to be gradually changed or varied, and that consequently it isnot essential that the inductance of the several self-induction coilsshall regularly diminish in one direction, or, what isthe same thing,increase in the other, or that there shall be any corresponding regularchange in the capacity value of the condensers, care being IOCsection-viz. ,that which is adapted to connect with theloaded-circuitconductor-to minimum impedance in the other end section,where connection may be made with the unloaded continuation-circuitconductor.

Fig. 2 illustrates a construction of the taporing apparatus wherein theinductance.

coils H H H of the several impedance-sections of gradually-changingvalue are each provided with a separate iron core m, two similarwindings being wound over each core for inclusion in the two sides 2 3of the circuit,respectively.u O is the final loading-coil of theregularly-loaded long-distance circuit L, and A the localized taperingapparatus as a whole, having its first impedance-section D united to thesaid loaded conductors and its last section E connected with theunloaded extension-circuit U. The gradually-lowering values of theseveral impedance-sections as their distance from the loaded portionincreases, which in Fig. 1 are indicated by different lengths, are hereindicated by different numbers of turns. Thus the two windings of coil Hare each indicated by five turns, those of H by four turns, and those ofH by three turns. The number of turns in each case thus shownhas,however, no significance,v

except as such an indication thatthe impedance of each following sectionin the direction of the instrumentsS is lessthan that of itspredecessor. The condensers It, 70 and k are here shown as being bridgedbetween the two circuit conductors, on which are strung theinductance-coilsin such manner that one of them is bridged on both sidesof each coil. i

As shown in Fig. 3, the several inductancecoils of the artificialtaperapparatus. may all be wound over a single iron core to .form ahighly-condensed structure. In this appliance N is an iron ring core ofwell-known character divided on each semicircular side into threesubdivisions of diverse size by partitions n. On each side of the saidcore the coils H H H occupy the largest, medium, andsmallestsubdivisions, respectively, and are strung along theirrespectiveconductors 4t and 5, which unite them serially, insuch manner that fromthe end D of the appliance the impedances of the several sectionsregularly and gradually diminish toward the end E. The condenser 70 isbridged between the said conductors at a point before the firstinduction-coil is reached, condensers k and k at successive. pointsbetween the coils H H and H H respectively, and condenser k at a pointposterior to the final coils H In practice, however, the partitions 11,may be disregarded or, in fact, dispensed with, and the windings of eachsection may and preferably will be distributed over a considerableportion of the core andover one another, care being taken; to bringoutloops between the sections for the attachment of thecondenserterminals. By this arrangement leakage losses which are liableto occur near the par titionswhere it is difficult to uniformlydistribute the windings are avoided. With a taper appliance of such formany practical number of subdivisions or impedance-sections may be formedupon the same core, a fact which promises distinct advantage, since theworking current losses where the total required inductance is wound overa single core are substantially less, than they would be were thesectional inductance-coils wound on separate cores.

In Figs. 4, 5, and 6, which diagrammatically represent plans forutilizing the tapering appliance or apparatus at a way-station, Fig. 4;illustrates a double-graduated or impedance tapering apparatusintroduced into the main circuit between two regularly-loaded portions LL thereof, 0 indicating the last loading-coil of division L, and CJthe'final loading-coil of division L The impedance taper A has itshighest impedance-sections, comprising the inductance-coils H andcapacities k, at the ends D E, and fromboth of the said ends thesuccessive sections H? W, H W, &c., diminish, thelowest impedance beingat the center, Where the station instrumentsin this instance atelephone-receiver T and a high-resistance secondary winding 2' of atransmitter induction-coilare bridged between the conductorset 5 of thelocalized taper apparatus, which conductors are joined at their ends D Ewith the corresponding conductors 2 3 of the loaded portions L L of thecircuit. The condensers in this case are shown as being bridged betweenthe two circuit-conductors 4.5 of the system at points within theinductance-coil windings, which in the said two conductors correspond,the said points being at or near the centers of the said windings. Suchan alternative arrangement may in any particular case be adopted, ifpreferred. .Fig. 5 represents a slightly-different plan, wherein thelocalized impedance or taper appliance forms a series connection at oneend E with the unloaded continuation circuit orinstrument loop U,extending there from to the station instruments S, and a bridgeconnection at points or y between any two of the regular loading-coils CC with the main line or regularly-loaded portion of the circuit. In thiscase not merely the station Ico instruments but also the entire systemof tapering impedance is bridged and the waystation communicates ineither direction with equal facility. In Fig. 6 the two divisions L L ofthe loaded line portion are shown as being normally connected through byswitchboard devices, (represented as switch-cord conductors s 8 whichhave their terminal plugs placed in switch-sockets 7 9 and 8 10,respectively. Obviously the plugs at either end of the said cords may bewithdrawn from their sockets and inserted instead in the switch-sockets12 13 of the impedance taper ing apparatus. By this plan when thestation instruments S are connected through the taper to the loadeddivision L or L on either hand the other of said divisions will be forthe time disconnected.

In the practice of this invention the total reflection loss in theentire localized tapering apparatus or system, or, in other words, thesum of the several reflection losses of the several progressive steps,is small in comparison with the loss occurring when no such taperingsystem or when no competent substitute, such as a terminal transformer,is provided and when therefore the transition from the loaded to theunloaded portions of the circuit, or vice versa, is precipitous.

It has been experimentally ascertained that the practical advantageattending the employment of the taper is perceptibly greater than thatobtained from the use of the best terminal transformer thus fardesigned.

Since the employment of such terminal transformers has to some extentbeen found to hamper the simultaneous use of telephone-circuits forother purposes (such as telegraphy) by reason of the solution ofconductive continuity introduced by them, an added (albeit incidental)advantage attending the present invention in association with loadedlines is that by its use the said transformers may be altogetherdispensed with. Furthermore, it has also been found that suchattenuation of the working current as occursin and by reason of theimpedance tapering apparatus itself is so slight as to be practicallynegligible.

Having thus described our invention, we claim 1. A localized or stationtaper for loaded electric circuits, comprising a series of gradtally-varying impedance elements composed of inductance-coils andcondensers adapted to be interposed in the circuit between the loadedline portion thereof and the station instruments, and constituting anartificial loaded and graduated reflection reducing extension of saidline-section, the magnitude or value of the said impedance elementsrespectively, being greatest toward the said loaded line-section, anddiminishing by successive steps toward the said instruments,substantially as described.

2. A localized and artificial tapering apparatus or system for a loadedelectric circuit adapted to be interposed in said circuit between theregularly-loaded portion thereof and an unloaded continuation orinstrument extension, and consisting as described, of a series ofimpedance sections or element-sconstituted each of resistance,inductance, and capacity so combined in each section, that the nearestsection to the said loaded portion of the circuit shall have a highimpedance approximating that of a corresponding section of loaded line,and that the following sections shall have impedances each smaller thanits predecessor and diminishing in substantially geometricallyprogressive steps to the section nearest to the said unloaded circuitcontinuation, substantially as described.

3. The combination in a concentrated arti* ficial taper extension for aloaded electric circuit, of a plurality of self-induction coils, acircuit-conductor electrically uniting the said coils in series andadapted to be interposed between the regularly-loaded line portion ofsuch loaded electric circuit and a station or continuation circuit, anda group of associated condensers in parallel branches of saidcircuit-conductor, the inductances and capacities of said coils andcondensers respectively being so relatively arranged and proportioned asto constitute a succession of balanced sections or elements of graduallyor progressively changing impedance, substantially as described. I

4. A graduated impedance appliance forming an artificial and localizedtaper for loaded electric circuits, and comprising a succession ofbalanced self-inductive windings wound over a single iron core andconnected in series to constitute a through-conductor, and a group ofassociated condensers in parallel branches of said conductor extendingfrom points in or between said windings, the said windings andcondensers being so arranged and proportioned as to constitute a seriesof separate successive sections varying gradually or by regular orprogressive steps from maximum impedance in one end section, to minimumimpedance in the other, substantially as described.

5. The combination with an electric circuit loaded with inductance-coilsconnected in the main conductor or conductors in series and at shortintervals, of a localized and concentrated artificial load taper placedat a station of said circuit between the regularly-loaded or mainportion thereof and a continuation circuit or instrument extension, andcomprising a series of sections or divisions gradually or progressivelydiminishing or tapering in impedance from the impedance value of saidregularly-loaded portion to that of said continuation or extension,substantially as and for the purposes set forth.

6. The combination with an electric circuit loaded with inductance-coilsconnected in the main conductor or conductors in series and twosubscribing witnesses, this 4th day of March, 1902. I

, HOWARD S. WARREN.

Witnesses:

GEo. WILLIS PIERCE, JOSEPH A. GATELY.

In testimony whereof I have signed my name to this specification, in thepresence of two subscribing witnesses, this 14th day of March, 1902.

GEORGE A. CAMPBELL. Witnesses:

GEO. WILLIS PIERCE, JOSEPH A. GATELY.

